Systems and methods for forming diamond heterojunction junction devices

ABSTRACT

A method of forming a p-n junction device comprises providing a base layer including a p-type diamond. A monolayer or few layer of a transition metal dichalcogenide (TMDC) is disposed on at least a portion of the base layer so as to form a heterojunction therebetween. The TMDC monolayer is an n-type layer such that the heterojunction between the intrinsic and p-type diamond base layer and the n-type TMDC monolayer is a p-n junction.

The United States Government claims certain rights in this inventionpursuant to Contract No. W-31-109-ENG-38 between the United StatesGovernment and the University of Chicago and/or pursuant toDE-AC02-06CH11357 between the United States Government and UChicagoArgonne, LLC representing Argonne National Laboratory.

TECHNICAL FIELD

The present disclosure relates generally to methods for fabricatingdiamond semi-conductor devices.

BACKGROUND

High-speed and high-power semiconductor device, are in great demand inthe telecommunication, power electronics, and solar inverter industries.The insatiable consumer demand for cutting-edge high-speed productfeatures creates opportunities for enabling technologies in thetelecommunications industry. In addition, the high-power/frequencydevices have many applications such as in microwave power amplifiersthat are widely used in civilian and military electronics. The increaseof power density and performance while simultaneously decreasing cost isa constant trend in the power semiconductor world.

Diamond has exceptional material attributes such as high thermalconductivity, breakdown voltage and carrier mobility, amongst otherfavorable enabling properties which make it a favorable candidate fornext-generation power electronics devices. However, high costsassociated with diamond, as well as technological issues such asachieving n-type doping have kept diamond-based semiconductor devicesfrom being commonly employed.

SUMMARY

Embodiments described herein relate generally to diamond semi-conductordevices and, in particular to diamond based p-n junction devices thatinclude a two dimensional transition metal dichalcogenide (TMDC) andmethods of fabricating the same.

In some embodiments, a method of forming a p-n junction device comprisesproviding a base layer including a p-type diamond. A monolayer of atransition metal dichalcogenide (TMDC) is disposed on at least a portionof the base layer so as to form a heterojunction therebetween. The TMDCmonolayer is an n-type layer such that the heterojunction between thep-type diamond base layer and the n-type TMDC monolayer is a p-njunction.

In some embodiments, a p-n junction device comprises a base layercomprising a p-type diamond. A monolayer of a transition metaldichalcogenide (TMDC) is disposed on at least a portion of the baselayer. The TMDC monolayer and the base layer form a heterojunctiontherebetween. Moreover, the TMDC monolayer is an n-type layer so thatthe heterojunction is a p-n junction.

In some embodiments, a method of forming a p-n junction device comprisesproviding a base layer including a p-type diamond. A monolayer of ametal dichalcogenide (TMDC) is disposed on at least a portion of thebase layer. An insulating layer is disposed on the TMDC monolayer andthe base layer. The insulating layer is patterned so as to expose atleast a portion of the TMDC monolayer and the base layer. A maskinglayer is disposed over the insulating layer and the TMDC layer. Themasking layer is patterned so as to expose at least a portion of theTMDC monolayer and the base layer. A conducting layer is disposed on themasking layer so as to contact the exposed portion of the TMDC layer.The masking layer is removed thereby removing only a portion of theconducting layer disposed on the masking layer. The TMDC monolayer is ann-type layer such that the heterojunction between the p-type diamondbase layer and the n-type TMDC monolayer is a p-n junction.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the subject matter disclosed herein. In particular, all combinationsof claimed subject matter appearing at the end of this disclosure arecontemplated as being part of the subject matter disclosed herein.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. Understanding thatthese drawings depict only several implementations in accordance withthe disclosure and are therefore, not to be considered limiting of itsscope, the disclosure will be described with additional specificity anddetail through use of the accompanying drawings.

FIG. 1 is a schematic flow diagram of an example method of fabricating adiamond p-n junction device.

FIG. 2 is a schematic block diagram of a process flow of another methodof fabricating a diamond p-n junction device.

FIG. 3 is a schematic illustration of a side cross-section of a p-njunction device according to an embodiment.

FIG. 4A is an optical image of a p-n junction device that includes amolybdenum disulfide (MoS₂) n-type layer positioned over a diamondsubstrate and contacted by electrodes; FIG. 4B is an enlarged opticalimage of a portion of the p-n junction device of FIG. 4A.

FIG. 5A is a current-voltage (I-V) plot of a first p-n diode thatincludes an ultrananocrystalline diamond (UNCD)-MoS₂ p-n junction; FIG.5B is an I-V curve of a second p-n diode that also includes a UNCD-MoS₂p-n junction.

FIG. 6A is an I-V curve a third p-n diode that includes a UNCD-MoS₂ p-njunction; FIG. 6B is semi-log I-V curve of the third p-n diode.

FIG. 7 is an I-V curve of a fourth p-n diode that includes ananocrystalline diamond (NCD)-MoS₂ p-n junction.

FIG. 8 illustrates a device fabrication flow where bulk pn junctions areformed on SC-CVD diamond sample in contrast to the B-UNCD fabricationflow of FIG. 2

FIG. 9A illustrates a cross-sectional geometry of a pn junctionformation with graphene/Pd/Au contacts on MoS₂; FIG. 9B illustrates across-sectional geometry of a pn junction formation with Ni/Au contactson MoS₂.

FIG. 10A shows IV characteristics of boron doped NCD/MoS₂ pn junction;FIG. 10B shows the semi-log plot of IV curves for the device of FIG.10A.

FIG. 11A is a graph of IV characteristics of boron doped SC-CVDdiamond/MoS₂ pn junction with Ti/Au contracts on MoS₂; FIG. 11B shows asemi-log plot of IV curves for the device of FIG. 11A; FIG. 11C shows CVcurves at different frequencies for the device of FIG. 11A.

FIG. 12A is a graph of IV characteristics of boron doped SC-CVDdiamond/MoS₂ pn junction with graphene/Ti/Au contracts on MoS₂; FIG. 12Bshows a semi-log plot of IV curves for the device of FIG. 12A.

FIG. 13A is a graph of IV characteristics of boron doped SC-CVDdiamond/MoS₂ pn junction with Ni/Au contracts on MoS₂; FIG. 13B shows asemi-log plot of IV curves for the device of FIG. 13A.

Reference is made to the accompanying drawings throughout the followingdetailed description. In the drawings, similar symbols typicallyidentify similar components, unless context dictates otherwise. Theillustrative implementations described in the detailed description,drawings, and claims are not meant to be limiting. Other implementationsmay be utilized, and other changes may be made, without departing fromthe spirit or scope of the subject matter presented here. It will bereadily understood that the aspects of the present disclosure, asgenerally described herein, and illustrated in the figures, can bearranged, substituted, combined, and designed in a wide variety ofdifferent configurations, all of which are explicitly contemplated andmade part of this disclosure.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

Embodiments described herein relate generally to diamond semi-conductordevices and, in particular to diamond based p-n junction devices thatinclude a two dimensional transition metal dichalcogenide (TMDC) andmethods of fabricating the same.

High-speed and high-power semiconductor devices are in great demand inthe telecommunication, power electronics, and solar inverter industries.The insatiable consumer demand for leading-edge high-speed productfeatures creates opportunities for enabling technologies in thetelecommunications industry. In addition, the high-power/frequencydevices have many applications in microwave power amplifiers that arewidely used in civilian and military electronics. The increase of powerdensity and performance while simultaneously decreasing cost is aconstant trend in the power semiconductor world.

While silicon is still the most popular semi-conductor material, wideband gap semiconductor materials such as silicon carbide and galliumnitride are of interest because of their superior material properties.However, processing issues and manufacturing costs associated with thesematerials create hurdles for replacing silicon with these materials.

Diamond has exceptional material attributes such as high thermalconductivity, breakdown voltage and carrier mobility, amongst otherfavorable enabling properties which make it a favorable candidate fornext-generation power electronics devices. For example, diamond has highthermal conductivity, excellent radiation hardness, high temperaturestability, low leakage current, high frequency and high power handlingcapability to name a few.

Although progress in chemical vapor deposition (CVD) technology hasallowed fabricating large size (e.g., 7.5 mm to 7.5 mm) single crystaldiamond wafers, it is difficult to n-dope diamond which is key toforming semi-conductor devices. Some process which use in-situ doping ofphosphorus during homoepitaxial growth (with moderate dopingconcentration of 1,018 cm⁻³ and mobility of 100 cm²/V-s operating at 150degrees Celsius) or with delta doping method of confining dopant layerwithin few nm to achieve high carrier concentration and mobility at roomtemperatures, are very complex and challenging and not readily amenableto large scale manufacturing processes.

Embodiments of diamond-TMDC p-n junction devices and methods of formingthe same may provide several benefits including, for example: (1)providing a monolayer of a TMDC on a p-doped diamond which serves as an-type “delta doped layer,” thereby eliminating the use of complexprocedures for doping a few nm thick layer of the p-doped diamond withhigh n-doping concentration; (2) enabling an excellent atomic interfacebetween the TMDC and diamond via van der Waal's interaction of the2-dimensional TMDC monolayer with the p-doped diamond; (3) enhancing thealready superior current density provided by TMDC materials (e.g., MoS₂having a current density of about 10⁷ amperes per cm²) by contacting theTMDC with the high thermal conductivity diamond; (4) easily scalable towafer scale, thereby allowing manufacturing of semi-conductor devices ona large scale; and (5) finding applications in several semi-conductorapplications such as photodetectors, rectifiers, solar cells,transistors, etc.

As used herein, the term “single crystal diamond (SCD)” refers tomonocrystalline diamond without any grain boundaries, and“nanocrystalline diamond (NCD)” refers to crystalline diamond that has agrain size in the range of 10 nm to 200 nm, and the term“ultrananocrystalline diamond (UNCD)” refers to crystalline diamond thathas a grain size in the range of 2 nm to 10 nm. Polycrystalline diamondmay be nanocrystalline or ultrananocrystalline. “Mono layer” means asingle layer. “Few layer” means at least two and at most 10 layers andranges inclusive therein.

FIG. 1 is a schematic flow diagram of an example method 100 for forminga p-n junction device. The method 100 includes providing a base layerincluding a p-type diamond at 102. For example, the base layer caninclude intrinsic or a p-doped SCD, p-doped NCD or a p-doped UNCD. Thebase layer may have any suitable shape or size. For example, the baselayer may include a diamond wafer (e.g., a 7.5 mm×7.5 mm SCD wafer), adiamond film, a diamond block or any other shape and size. Furthermore,the base layer may include a single crystal diamond or a polycrystallinediamond.

In some embodiments, the base layer may include a diamond (e.g.,intrinsic or a p-type SCD, NCD or a p-type UNCD diamond) deposited on asubstrate. The substrate can have any shape or size (e.g., a sheet, ablock, a wafer, etc.) and can be formed from any suitable material suchas, silicon, silicon carbide, glass, quartz, Pyrex, metals, polymers,oxides, etc. In such embodiments, the diamond may be deposited on thesubstrate using any suitable process (e.g., a microwave plasma chemicalvapor deposition process).

The diamond base layer may have any suitable thickness. In someembodiments, the diamond base layer may have a thickness in the range of1 micron to a 1,000 microns inclusive of all ranges and valuestherebetween. In other embodiments, the diamond base layer may have athickness in the range of 50 nms to about 150 nms (e.g., about 50 nms,60 nms, 70 nms, 80 nms, 90 nms, 100 nms, 110 nms, 120 nms, 130 nms, 140nms, or about 150 nms inclusive of all ranges and values therebetween).In some embodiments, the diamond base layer may have a root mean square(RMS) roughness of less than 10 nms. In particular embodiments, thediamond base layer may be sufficiently thin so as to have a transparencyof greater than about 90%, for example, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98% or about 99%.

As described before, the base layer includes intrinsic or a p-typediamond. In some embodiments, the diamond may be doped with a p-typedopant. Any suitable p-type dopant may be used, for example boron.Doping of the base layer with the p-type dopant may be performed usingany suitable process. For example, the p-type dopant may be implanted inthe diamond base layer which may be annealed thereafter.

In other embodiments, the diamond may be doped with the p-type dopantduring the diamond deposition process. For example, the p-type dopant(e.g., boron) may be introduced during the diamond deposition process(e.g., a boron gas introduced into a microwave plasma chamber used todeposit the diamond base layer on the substrate) so as to incorporateatoms of the p-type dopant into the diamond deposited on the substrate.

A monolayer or few layer (such as 2-10, in one embodiment, and rangesinclusive therein in other embodiments) of a TMDC is disposed on atleast a portion of the base layer at 104. Deposition may be bymechanical or chemical exfoliation or by a deposition technique such asCVD or ALD. The TMDC monolayer forms a heterojunction with the diamondbase layer. The TMDC includes an n-type layer such that theheterojunction between the p-type diamond base layer and the n-type TMDCmonolayer forms a p-n junction, thereby yielding the p-n junctiondevice. The TMDC may include any material having the chemical formula:

MX₂

where M is a transition metal such as molybdenum, scandium, titanium,tungsten, chromium, manganese, iron, cobalt, nickel, copper, zinc,vanadium, or any other transition metal, and X is a chalcogen atom, forexample sulfur, selenium, tellurium, oxygen or polonium.

For example, the TMDC monolayer may include molybdenum disulfide (MoS₂).MoS₂ is a direct band-gap material when it is in monolayer form, and hasa bandgap of about 1.9 electron Volts (eV). It is naturally n-typematerial with carrier mobilities which may be as high as 450 cm²/V-s. Ithas a high current density of about 5×10⁷ amperes per cm², which may beextended even further on the high thermal conductivity diamond baselayer. It is stable at high temperature, has stiffness greater thansteel, and is flexible and transparent. Moreover, MoS₂ may demonstrateambipolar characteristics which are suitable for forming electronicdevices.

A monolayer of MoS₂ may be about 1 nm thick and essentially mimics anultrathin delta doped n-type layer on diamond. Therefore, depositing then-type MoS₂ monolayer or any other TMDC monolayer on the diamond baselayer may result in a p-n junction between the TMDC (e.g., MoS₂) and thediamond. The atomically thin TMDC monolayer provides pristine surfacequality and lacks dangling bonds. The van der Waal's interaction betweenthe TMDC monolayer and the diamond base layer forms the heterojunctionwhich has a perfect atomic interface between the diamond base layer andthe TMDC monolayer so as to result in an effective p-n junction.

The TMDC monolayer or few layer may be disposed on the diamond baselayer using any suitable method. In some embodiments, the TMDC monolayermay be disposed using mechanical exfoliation. For example, the TMDCmonolayer may be exfoliated from a bulk MoS₂ (e.g., via scotch tapemechanical exfoliation). The exfoliated layer is then transferred to thediamond substrate. In other embodiments, the MoS₂ may be deposited usingchemical vapor deposition (CVD), sputtering, thermal evaporation,electron beam evaporation, atomic layer deposition (ALD), chemicalself-assembly or any other suitable method.

In some embodiments, an insulating layer may be disposed on the baselayer and the TMDC monolayer at 106. The insulating layer may includealuminum oxide, hexagonal boron nitride, silicon oxide, silicon nitrideor any other suitable insulating material. The insulating layer may bedisposed on the base layer and the TMDC monolayer using any method, forexample CVD, ALD, sputtering, spin coating, chemical self-assembly orany other suitable method. The insulating layer may have any suitablethickness, for example in the range of 1 nm to 100 nm inclusive of allranges and values therebetween (e.g., about 50 nm). In particularembodiments, the insulating layer may have a sub-nanometer thickness.

The insulating layer is patterned so as to expose at least a portion ofeach of the TMDC monolayer and the base layer at 108. For example, theinsulating layer may be patterned using a combination ofphotolithography and etching (e.g., plasma etching or chemical etching),nanolithography, using a virtual mask (e.g., a computer generated maskpattern for patterning using e-beam lithography), e-beam lithography,ion-beam lithography or any other patterning method or a combinationthereof. In some embodiments, the exposed portion of the insulatinglayer and the base layer may serve to provide electrical contacts toeach of the p-type base layer and the n-type TMDC monolayer which formthe p-n junction.

In some embodiments, a conducting layer may be disposed on the exposedportions of the TMDC monolayer and the diamond base layer so as toprovide electrical contacts for interfacing the p-n junction device withexternal electronics. For example, the method 100 may include disposinga masking layer over the TMDC monolayer and the diamond base layer at110. The masking layer may include, for example a positive photoresist(e.g., any of the AZ® series photoresists, phenolic resins, etc.)negative photoresists (e.g., SU-8, AZ® nLOF 2000 series, e-beamphotoresists) or any other masking layer. The masking layer may bedeposited via spin coating, spray coating, vapor deposition or any othersuitable method.

The masking layer is patterned so as to expose the portions of thediamond base layer and the TMDC monolayer which do not have theinsulating layer disposed thereon at 112. For example, the masking layermay be patterned using a photolithography, e-beam lithography, physicaletching, chemical etching, nanoimprint lithography, any other method orcombination thereof. The patterning thereby removes the mask from theportions of the diamond base layer and the TMDC monolayer which do nothave the insulating layer disposed thereon.

A conducting layer is disposed on the masking layer at 114. Theconducting layer may form a film which contacts the exposed portions ofthe TMDC monolayer and the diamond base layer but is disposed on themasking layer at other portions of the film. The conducting layer mayinclude any suitable conductive layer which can form a strong electricalcoupling with the TMDC and the diamond base layer. For example, theconducting layer may include nickel, titanium, gold, platinum, 1T phasemolybdenum disulfide, graphene or any other suitable conducting layer.

The masking layer is removed so as to lift-off or remove only theportion of the conducting layer disposed on the masking layer at 116.This leaves the conducting layer disposed on in contact with the exposedportions of the TMDC monolayer and the diamond base layer. Theconducting layer may be used to form contacts with external electronics.

FIG. 2 is a schematic block diagram of a process for forming aparticular p-n junction device. At step 1 a base layer including ap-type diamond is provided and a MoS₂ monolayer is disposed on a portionof the base layer. The p-type diamond may include a p-type NCD or ap-type UNCD. The base layer may have any suitable shape or size. Forexample, the base layer may include a diamond wafer (e.g., a 7.5 mm×7.5mm diamond wafer), a diamond film, a diamond block or any other shapeand size. Furthermore, the base layer may include a single crystaldiamond or a polycrystalline diamond.

The diamond base layer may have any suitable thickness. In someembodiments, the diamond base layer may have a thickness in the range of1 micron to a 1,000 microns inclusive of all ranges and valuestherebetween. In other embodiments, the diamond base layer may have athickness in the range of 50 nms to about 150 nms (e.g., about 50 nms,60 nms, 70 nms, 80 nms, 90 nms, 100 nms, 110 nms, 120 nms, 130 nms, 140nms, or about 150 nms inclusive of all ranges and values therebetween).In some embodiments, the diamond base layer may have a root mean square(RMS) roughness of less than 10 nms. In particular embodiments, thediamond base layer may be sufficiently thin so as to have a transparencyof greater than about 90%, for example, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98% or about 99%.

The monolayer or few layers of MoS₂ may be about 1-10 nm thick andessentially mimics an ultrathin delta doped n-type layer on diamond. Then-type MoS₂ layer forms a heterogeneous interface with the p-typediamond layer, thereby forming a p-n junction therebetween. The van derWaal's interaction between the TMDC monolayer and the diamond base layerforms a heterojunction having a perfect atomic interface between thediamond and the TMDC so as to result in a high quality p-n junction.

The MoS₂ monolayer may be deposited on the diamond base layer using anysuitable method. In some embodiments, the MoS₂ monolayer may be disposedusing mechanical exfoliation. For example, the MoS₂ monolayer may beexfoliated from a bulk MoS₂ (e.g., via scotch tape mechanicalexfoliation). The exfoliated layer is then transferred to the diamondsubstrate. In other embodiments, the MoS₂ may be deposited usingchemical vapor deposition (CVD), sputtering, thermal evaporation,electron beam evaporation, atomic layer deposition (ALD), chemicalself-assembly or any other suitable method.

At step 2, an aluminum oxide (Al₂O₃) insulating layer is disposed on thebase layer and the TMDC monolayer. In other embodiments, the insulatinglayer may include hexagonal boron nitride, silicon oxide, siliconnitride or any other suitable insulating material. The insulating layermay be disposed on the base layer and the MoS₂ monolayer using anymethod, for example CVD, ALD, sputtering, spin coating, chemicalself-assembly or any other suitable method. The insulating layer mayhave any suitable thickness, for example in the range of 1 nm to 100 nminclusive of all ranges and values therebetween. In some embodiments,the Al₂O₃ insulating layer has a thickness of about 50 nm. In particularembodiments, the insulating layer may have a sub-nanometer thickness.

At step 3, the Al₂O₃ insulating layer is patterned so as to expose atleast a portion each of the TMDC monolayer and the diamond base layer.For example, the insulating layer may be patterned using a combinationof photolithography and etching (e.g., plasma etching or chemicaletching), nanolithography, using a virtual mask (e.g., a computergenerated mask pattern for patterning using e-beam lithography), e-beamlithography, ion-beam lithography or any other patterning method or acombination thereof.

In particular embodiments, the insulating layer includes Al₂O₃ which ispatterned using a combination of photolithography (e.g. using a positiveor negative photoresist) and wet etching with buffered hydrofluoric acid(BHF). The exposed portion of the insulating layer and the diamond baselayer may serve to provide electrical contacts to each of the p-typebase layer and the n-type TMDC monolayer which form the p-n junction.

At step 4, a titanium/gold (Ti/Au) conducting layer is disposed on theexposed portions of the TMDC monolayer and the diamond base layer so asto provide electrical contacts for interface of the p-n junction devicewith external electronics. For example, a masking layer may be disposedover the MoS₂ monolayer and the p-type diamond base layer. The maskinglayer may include, for example a positive photoresist (e.g., any of theAZ® series photoresists, phenolic resins, etc.) negative photoresists(e.g., SU-8, AZ® nLOF 2000 series, e-beam photoresists) or any othermasking layer. The masking layer may be deposited via spin coating,spray coating, vapor deposition or any other suitable method.

The masking layer is patterned so as to expose the portions of the baselayer and the MoS₂ monolayer which do not have the insulating layerdisposed thereon. The masking layer may be patterned using aphotolithography, e-beam lithography, physical etching, chemicaletching, nanoimprint lithography, any other suitable method orcombination thereof.

The Ti/Au conducting layer is then disposed on the masking layer. TheTi/Au conducting layer may form a film which contacts the exposedportions of the MoS₂ and the p-type base layer but is disposed on themasking layer at other portions of the film. The Ti/Au conducting layermay include an suitable conductive material which can form a strongelectrical contact with the MoS₂ and the p-type diamond base layer. Inother embodiments, the conducting layer may include any other conductingmaterial, for example nickel, platinum, 1T phase molybdenum disulfide,graphene or any other suitable conducting layer.

The masking layer is removed so as to lift-off or remove only theportion of the Ti/Au conducting layer disposed on the masking layer.This leaves the Ti/Au conducting layer disposed on and in contact withthe exposed portions of the MoS₂ monolayer and the p-type diamond baselayer. The Ti/Au conducting layer may be used to form contacts withexternal electronics.

FIG. 3 is a schematic illustration of a side cross-section of a p-njunction device 200 according to an embodiment. The p-n junction device200 may be formed using any of the methods described herein, for examplethe method 100. Furthermore, the p-n junction device 200 may be used inor form a sub-component of any semi-conductor device such as solarcells, photocells, rectification diodes, tunnel diodes, zener diodes,LEDs, PIN diodes, transistors, metal oxide semi-conductor field effecttransistors (MOSFET), sensors (e.g., Hall effect sensors), integratedcircuits, charge coupled devices (CCDs), ROMs, RAMs, etc.

The p-n junction device 200 includes a base layer 210. The base layer210 includes a p-type diamond, for example a p-type NCD or a p-typeUNCD. The base layer 210 may have any suitable shape or size. Forexample, the base layer 210 may include a diamond wafer (e.g., a 7.5mm×7.5 mm diamond wafer), a diamond film, a diamond block or any othershape and size. Furthermore, the base layer 210 may include a singlecrystal diamond or a polycrystalline diamond.

The base layer 210 may have any suitable thickness. In some embodiments,the base layer 210 may have a thickness in the range of 1 micron to a1,000 microns inclusive of all ranges and values therebetween. In otherembodiments, the base layer 210 may have a thickness in the range of 50nms to about 150 nms (e.g., about 50 nms, 60 nms, 70 nms, 80 nms, 90nms, 100 nms, 110 nms, 120 nms, 130 nms, 140 nms, or about 150 nmsinclusive of all ranges and values therebetween). In particularembodiments, the diamond base layer 210 may be sufficiently thin so asto have a transparency of greater than about 90%, for example, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98% or about 99%. While not shown, in someembodiments, the base layer 210 may be disposed on a substrate such as,silicon, glass, quartz, Pyrex, metals, polymers, oxides or any othersuitable substrate.

A TMDC monolayer 220 is disposed on the base layer 210. The TMDCmonolayer 220 forms a heterojunction with the base layer 210. The TMDCmonolayer 220 includes an n-type layer such that the heterojunctionbetween the base layer 210 and the TMDC monolayer 220 forms a p-njunction, thereby yielding the p-n junction device 200. The TMDCmonolayer 220 may include any material having the chemical formula:

MX₂

where M is a transition metal such as molybdenum, scandium, titanium,tungsten, chromium, manganese, iron, cobalt, nickel, copper, zinc,vanadium, or any other transition metal, and X is a chalcogen atom, forexample sulfur, selenium, tellurium, oxygen or polonium.

The TMDC monolayer 220 may be about 1 nm thick and essentially mimics anultrathin delta doped n-type layer on diamond. The TMDC monolayer 220may be deposited on the diamond base layer 210 using any suitablemethod, for example as described with respect to the method 100.

A first contact pad 230 is disposed on at least a portion of the TMDCmonolayer 220 and in electrical communication thereto. A second contactpad 240 is disposed on a second surface of the base layer 210 oppositethe TMDC monolayer 220, and in electrical communication with the baselayer 210. The first contact pad 230 and the second contact pad 240 mayallow electrical coupling of the TMDC monolayer 220 and the base layer210 with external electronics.

FIG. 3 shows the second contact pad 240 disposed on the second surfaceof the base layer 210. In some embodiments, the second contact pad 240may be disposed on a first surface of the base layer 210 on which theTMDC monolayer 220 is disposed. The first contact pad 230 and the secondcontact pad 240 may be disposed on the TMDC monolayer 220 and the baselayer 210 using any suitable method, for example as described withrespect to the method 100.

The first contact pad 230 and the second contact pad 240 may include ansuitable conductive layer which can form a strong electrical couplingwith the TMDC monolayer 220 and the p-type diamond base layer 210. Forexample, the first contact pad 230 and the second contact pad 240 mayinclude nickel, titanium, gold, platinum, 1T phase molybdenum disulfide,graphene or any other suitable conducting material.

In particular embodiments, an insulating layer may also be disposed onthe exposed portions of the TMDC monolayer 220 and/or the base layer210. The insulating layer may include aluminum oxide, hexagonal boronnitride, silicon oxide, silicon nitride or any other suitable insulatingmaterial. The insulating layer may be disposed on the diamond base layer210 and the TMDC monolayer 220 using any method, for example CVD, ALD,sputtering, spin coating, chemical self-assembly or any other suitablemethod as described with respect to the method 100. The insulating layermay have any suitable thickness, for example in the range of 1 nm to 100nm inclusive of all ranges and values therebetween (e.g., about 50 nm).In particular embodiments, the insulating layer may have a sub-nanometerthickness.

FIG. 4A is an optical image of a p-n junction device that includes amolybdenum disulfide (MoS₂) n-type layer positioned over a diamondsubstrate and contacted by electrodes, and FIG. 4B is an enlargedoptical image of a portion of the p-n junction device of FIG. 4A. Thep-n junction device includes a pair of Ti/Au electrodes disposed on ap-type diamond substrate. The electrodes are separated by a small gapbetween which a MoS₂ flake is disposed.

The MoS₂ flake shown in FIGS. 4A-B is disposed using mechanicalexfoliation. In other embodiments, the MoS₂ flake may be disposed usingCVD or any other suitable method as described herein. At least one ofthe pair of electrodes is in contact with the MoS₂ flake, while theother electrode is in contact with the p-type diamond substrate. TheMoS₂ flake is a monolayer thick (e.g., having a thickness of about 1 nm)and is inherently n-type such that the MoS₂ forms a delta doped p-nheterojunction with the p-type diamond.

Various devices similar to the device shown in FIGS. 4A-B werefabricated which included a UNCD base layer and a MoS₂ monolayerdisposed thereon so as to form a p-n diode. I-V characteristics of thep-n diodes were determined. FIG. 5A is an I-V plot of a first p-n diodewhich includes a p-type UNCD base layer and MoS₂ monolayer disposedthereon. The first p-n diode had a rectification ratio of 5 at a biasingvoltage of 9 Volts and an ideality factor “n” close to 60. FIG. 5B is anI-V plot of a second p-n diode which includes a p-type UNCD base layerand a MoS₂ monolayer disposed thereon. The second p-n diode had arectification ratio of 10 at a biasing voltage of 4 Volts and anideality factor “n” close to 40. It should be appreciated that thecurrent density and rectification ratios for NCD, UNCD, and SCD differ.

FIG. 6A is an I-V plot of a third p-n diode which includes a p-type UNCDbase layer and MoS₂ monolayer. The third p-n diode ha a rectificationratio of 15 at a biasing voltage of 5 Volts and an ideality factor n ofabout 14. FIG. 6B is a semi-log I-V plot of the third p-n diode.

FIG. 7 is an I-V plot of a fourth p-n diode which includes a p-type NCDbase layer and a MoS₂ monolayer. The fourth p-n diode had arectification ratio of 5 at a biasing voltage of 5 Volts and an idealityfactor n of about 70.

EXPERIMENTS

In order to study the formation of p-n junctions, experiments describedbelow were undertaking. The general technique is shown in FIG. 1 andFIG. 2.

The MoS₂ flakes are mechanically exfoliated using a scotch tape onto theB-doped nanocrystalline diamond (NCD) and B-doped singlecrystalline-chemical vapor deposited (SC-CVD) diamond samples. The NCDhas resistivity of 9.25E-2 Ohms-cm and sheet resistance of 9.86E2Ohms/square and B-doped SC-CVD diamond has a doping concentration of2.1E15/cm3. The exfoliated flakes on diamond suitable for devicefabrication are identified and characterized using: optical microscopy,Raman spectroscopy, AFM and SEM. Aluminum oxide with thickness of 50 nmis deposited on the whole sample using atomic layer deposition (ALD) toact as passivation layer. A laser pattern generator (photolithography)is used to pattern to etch the Al₂O₃ on the identified flakes formetallization. Ti/Au contacts are deposited by using e-beam evaporationafter an additional step of lithography. FIG. 2 illustrates the B-UNCDformation method utilized for comparative purposes. The B-SC-CVD devicefabrication flow is shown in FIG. 8. Lateral pn junctions are fabricatedon NCD substrates, while bulk pn junctions are formed on SC-CVD diamondsample. In some embodiments, a back contact of Ti/Pt/Au is deposited. Inone particular embodiment, the Ti/Pt/Au contact has thickness of10/10/80 nm and is deposited using e-beam evaporation.

The integration of 2D materials with diamond (3D) by forming aheterojunction was studied experimentally. Further studies are requiredfor a detailed understanding of the transport phenomena at theinterface. This can be further studied by addressing the issues such asseries resistance, improving the contacts on 2D MoS₂ and diamondsubstrates. However, the initial results are encouraging towardsfabrication of 2D/3D heterojunction devices by integrating p-typediamond with n-type 2D MoS₂. A more detailed study is done on SC-CVDdiamond sample by employing different contacts on the MoS₂ flakes.Contacts such as graphene/Pd/Au and Ni/Au are deposited. For graphenedeposition, a transfer method using PMMA is used. The geometry of thedevice can be seen in FIG. 9B.

RESULTS AND DISCUSSION

The IV curves obtained are shown in FIG. 10A-12B. A strong rectificationbehavior can be observed from the curves. The rectification ratio iscalculated as close to 15 with an ideality factor calculated from thediode equation is around 14 for the NCD/MoS₂ structures. Although theideality factor is high, the results are still encouraging enough forpreliminary studies. The high ideality factor is due to therecombination current arising from defects/traps at the interface, highseries resistance from the substrate and high contact resistance on MoS₂layers.

For the SC-CVD diamond/MoS₂ structures with Ti/Au contacts, arectification ratio of 211, ideality factor of 14 and current density:102 Amps/cm₂ were observed at 8 V. CV measurements for this structureare plotted in FIG. 11c . The measurements were made at differentfrequencies and high frequency dispersion is observed indicatinginterface states and a high series resistance. These measurements alsoreflect the high ideality factor calculated from the IV curves.Furthermore, by changing the contacts to graphene/Pd/Au, therectification has improved to 270 with an ideality factor of 9. Thecurrent density obtained is 1005 Amps/cm₂ which is a few orders morethan in the previous case.

An additional study of the SC-CVD diamond/MoS₂ was done by employing adifferent geometry and contacts with Ni/Au as shown in FIG. 9B. Therectification ratio has further improved a few orders of magnitude to10E6, with an ideality factor of 4 and forward current density of 1130Amps/cm₂ at 8 V. Capacitance voltage (CV) measurements of the devicefrom have been performed to look at the doping concentrations andbuilt-in voltage of the device.

Definitions

As used herein, the singular forms “a”, “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, the term “a member” is intended to mean a single member or acombination of members, “a material” is intended to mean one or morematerials, or a combination thereof.

As used herein, the terms “about” and “approximately” generally meanplus or minus 10% of the stated value. For example, about 0.5 wouldinclude 0.45 and 0.55, about 10 would include 9 to 11, about 1000 wouldinclude 900 to 1100.

It should be noted that the term “exemplary” as used herein to describevarious embodiments is intended to indicate that such embodiments arepossible examples, representations, and/or illustrations of possibleembodiments (and such term is not intended to connote that suchembodiments are necessarily extraordinary or superlative examples).

The terms “coupled,” “connected,” and the like as used herein mean thejoining of two members directly or indirectly to one another. Suchjoining may be stationary (e.g., permanent) or moveable (e.g., removableor releasable). Such joining may be achieved with the two members or thetwo members and any additional intermediate members being integrallyformed as a single unitary body with one another or with the two membersor the two members and any additional intermediate members beingattached to one another.

It is important to note that the construction and arrangement of thevarious exemplary embodiments are illustrative only. Although only a fewembodiments have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Othersubstitutions, modifications, changes and omissions may also be made inthe design, operating conditions and arrangement of the variousexemplary embodiments without departing from the scope of the presentinvention.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinventions or of what may be claimed, but rather as descriptions offeatures specific to particular implementations of particularinventions. Certain features described in this specification in thecontext of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresdescribed in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

1. A method of forming a heterojunction or p-n junction device,comprising: providing a base layer including intrinsic or a p-typediamond; and disposing, by mechanical exfoliation, a 1-10 layers of atransition metal dichalcogenide (TMDC) on at least a portion of the baselayer so as to form a TMDC layer and a heterojunction therebetween,wherein the TMDC layer is an n-type layer such that the heterojunctionbetween the p-type diamond base layer and the n-type TMDC monolayer is ap-n junction.
 2. The method of claim 1, wherein the TMDC layer includesmolybdenum disulfide.
 3. The method of claim 1, wherein the p-typediamond base layer includes at least one of an intrinsic or p-typesingle crystal diamond, p-type polycrystalline diamond.
 4. The method ofclaim 1, wherein the p-type diamond base layer is doped with boron. 5.(canceled)
 6. (canceled)
 7. The method of claim 1, further comprising:disposing an insulating layer on the TMDC monolayer and the base layer;and patterning the insulating layer so as to expose at least a portionof the TMDC monolayer.
 8. The method of claim 7, wherein the insulatinglayer includes at least one of aluminum oxide, hexagonal boron nitride,silicon oxide or silicon nitride.
 9. The method of claim 7, furthercomprising: disposing a conducting layer on at least a portion of thebase layer and the exposed portion of the TMDC monolayer so as to formelectrical contacts with each of the base layer and the TMDC monolayer.10. The method of claim 9, wherein the conducting layer includes atleast one of nickel, titanium, gold, platinum, 1T phase molybdenumdisulfide and graphene.
 11. A p-n junction device, comprising: a baselayer comprising a p-type diamond; and a monolayer or few layer of atransition metal dichalcogenide (TMDC) disposed on at least a portion ofthe base layer forming a TMDC layer, the TMDC layer and the p-typediamond forming a heterojunction therebetween, an electrical contact padphysically contacting and electrically coupled to the base layer and theTMDC layer; wherein the TMDC layer is an n-type layer so that theheterojunction is a p-n junction.
 12. The p-n junction device of claim11, wherein the base layer and at least a portion of the TMDC layer iscoated with an insulating layer.
 13. The p-n junction device of claim12, wherein the insulating layer includes at least one of aluminumoxide, hexagonal boron nitride, silicon oxide or silicon nitride. 14.(canceled)
 15. The p-n junction device of claim 11, wherein the baselayer is positioned on a substrate.
 16. The p-n junction device of claim11, wherein the p-type diamond includes at least one of a p-typenanocrystalline diamond and a p-type ultrananocrystalline diamond. 17.The p-n junction device of claim 11, wherein the TMDC layer includesmolybdenum disulfide.
 18. A method of forming a p-n junction device,comprising; providing a base layer including a p-type diamond; disposingat least one layer and at most 10 layers of a metal dichalcogenide(TMDC) on at least a portion of the base layer to form a TMDC layer;disposing an insulating layer on the TMDC layer and the base layer;patterning the insulating layer so as to expose at least a portion ofthe TMDC layer; disposing a masking layer over the insulating layer andthe TMDC layer; patterning the masking layer so as to expose at least aportion of the TMDC layer and the base layer; disposing a conductinglayer on the masking layer so as to contact the exposed portion of theTMDC layer and the base layer; and removing the masking layer therebyremoving only a portion of the conducting layer disposed on the maskinglayer, wherein the TMDC layer is an n-type layer such that theheterojunction between the p-type diamond base layer and the n-type TMDClayer is a p-n junction.
 19. The method of claim 18, wherein the TMDClayer includes a molybdenum disulfide.
 20. The method of claim 18,wherein the p-type diamond includes at least one of a p-typenanocrystalline diamond and a p-type ultrananocrystalline diamond. 21.The method of claim 18, wherein the TMDC layer is formed on the portionof the base layer using chemical vapor deposition.